The present invention relates generally to circuitry for controlling automotive airbag or Supplemental Inflatable Restraint Systems, and more particularly, to circuitry for detecting non-deployment conditions in seemingly deployable circumstances and inhibiting deployment of the airbag based on detection of such conditions.
Airbags are commonplace in automotive vehicles as a result of the need to improve occupant safety in collisions. In fact, airbags are standard equipment in many, if not most, late model automotive vehicles. These airbags are typically located in strategic places, such as the steering wheel of a vehicle, and are intended to help reduce occupant injury in the event of a crash. In general, airbag management requires specialized systems for detecting collisions, deploying airbags when appropriate, and also inhibiting airbag deployment when the crash is not sufficiently severe to warrant airbag deployment.
Airbag management systems typically include at least one acceleration sensor, commonly referred to as an accelerometer, to sense acceleration/deceleration along a specific axis. Deployment of the airbag generally occurs only when the accelerometer senses at least a minimum acceleration along an appropriate axis. Typically, an airbag management system includes a number of accelerometers for sensing acceleration along a corresponding number of axes.
In the operation of typical airbag management systems, an accelerometer senses acceleration and produces an acceleration signal, wherein the acceleration signal is processed via a decision circuit to determine whether airbag deployment is warranted. Generally, however, great care must be exercised in designing such systems to avoid inadvertent airbag deployment. Inadvertent airbag deployment is not only costly, as the result of having to repair and replace the deployed airbag, but it can also create a potentially dangerous situation for the occupants. For example, inadvertent deployment may force the driver out of position or otherwise impair the driver""s ability to safely operate the vehicle. To reduce the possibility of inadvertent airbag deployment, some airbag management systems include a redundant xe2x80x9carmingxe2x80x9d sensor (e.g., accelerometer) operable to alert the system of a potential deployment condition only if the crash is above a crash severity threshold.
Referring to FIG. 1, one known airbag management system 100 is shown including such a redundant arming sensor 110. System 100 also includes at least one accelerometer 120 suitably positioned for controlling a corresponding airbag. The accelerometer 120 senses and transduces an acceleration 130 into an analog acceleration signal proportional to the amount of acceleration sensed, typically measured in multiples of gravitation force units denoted by the symbol G.
The accelerometer 120 provides the analog acceleration signal to an analog to digital (A/D) converter 140 via signal path 122 which converts the signal to a digital acceleration signal and provides this digital signal to a microprocessor 150 via signal path 142. The microprocessor 150 is electrically connected to a deployment circuit 160 via signal path 154 which is itself electrically connected to an inhibit deployment circuit 170 electrically connected to arming sensor 110 via signal path 112. An output of the inhibit deployment circuit 170 is connected to an actuator (not shown) of an airbag 174 via signal path 172.
The microprocessor 150 typically includes a deployment control algorithm 152 for determining whether the digital acceleration signal on signal path 142 is of sufficient magnitude to deploy airbag 174, and provides a signal corresponding thereto to the deployment circuit 160. The arming sensor 110 is also operable to sense acceleration and provide a corresponding acceleration signal to the inhibit deployment circuit 170. Typically, the arming sensor 110 is configured to provide greater resolution in the lower G ranges, and the inhibit deployment circuit 170 is operable to process this signal to determine whether the crash event is sufficiently severe to allow deployment of the airbag 174. If, for example, the inhibit deployment circuit 170 determines that the acceleration signal produced by arming sensor 110 is below a predefined G threshold, circuit 170 is operable to inhibit any deployment signal produced by deployment circuit 160 on signal path 162 so that the airbag 174 is not deployed. If, on the other hand, the inhibit deployment circuit 170 determines that the acceleration signal produced by arming sensor 110 is above the predefined G threshold, circuit 170 is operable to pass any deployment signal produced by deployment circuit 160 to airbag 174 via signal path 172 to thereby deploy the airbag 174.
The airbag management system 100 just described includes a multitude of components including the arming sensor 110. These components increase the cost and complexity of system 100. Further, as the number of accelerometers 120 increase, the number of arming sensors 110 increases linearly. Therefore, for every accelerometer 120 located in the vehicle to sense along a certain axis, an arming sensor 110 must be located along the same axis, and preferably in close proximity to the accelerometer. Not only is this cost restrictive, physically locating these devices in close proximity is oftentimes impractical and sometimes impossible. Moreover, physical and electronic constraints of standard microprocessors limit the number of accelerometers that the system can manage. As more accelerometers are added, processing time becomes a constraint and thus unacceptable delays in the deployment of the airbag ensue, thereby compromising the safety of the occupants of the vehicle.
Referring now to FIG. 2, another known airbag management system 180 is shown that eliminates the need for arming sensor 110 but that incorporates and implements the arming sensor""s functions into a microprocessor 190. System 180 includes many of the same components as system 100 of FIG. 1, and like components are therefore identified with like reference numbers. For example, an accelerometer 120 is responsive to an acceleration 130 to produce an analog acceleration signal on signal path 122. An A/D converter 140 is operable to convert the analog acceleration signal on signal path 122 to a digital acceleration signal and provide this digital acceleration signal on signal path 142. Microprocessor 190 is responsive to the digital acceleration signal on signal path 142 to produce a deployment control signal on signal path 194 if a crash of sufficient severity is detected, in accordance with deployment control algorithm 152 as described hereinabove. A deployment circuit 170 is, in turn, responsive to the deployment control signal on signal path 194 to produce a corresponding drive signal on signal path 172 to thereby deploy air bag 174.
In addition to algorithm 152, the microprocessor 190 is also programmed to assume the function of the arming sensor 110 of FIG. 1 by including a software algorithm 192 operable to determine the magnitude of the digital acceleration signal on signal path 142 and assess whether this magnitude is sufficiently large along the proper axis to cause the deployment control algorithm (e.g., algorithm 152) to produce an active deployment control signal for deploying the air bag 174.
Referring to FIG. 3, a flowchart illustrating one known embodiment of a software algorithm 200, resident within microprocessor 190 of FIG. 2, is shown, wherein algorithm 200 is operable to process the digital acceleration signal and determining whether to deploy, or inhibit deployment of, the airbag 174. The algorithm 200 thus incorporates therein both the deployment control algorithm 152 program and algorithm 192 described with respect to FIG. 2. At step 202, the digital acceleration signal is received, and at step 204, the algorithm processes the digital acceleration signal in an known manner to determine whether to deploy the airbag 174. Step 204 thus corresponds to the execution of the deployment control algorithm 152. Thereafter at step 206, if the microprocessor 190 determines that airbag deployment is not warranted, algorithm execution advances to step 214 to inhibit airbag deployment. If, however, microprocessor 190 determines at step 206 that airbag deployment is warranted, algorithm execution advances to step 208 where microprocessor 190 is operable to calculate a time rate of change of the digital acceleration signal, preferably by comparing the absolute value of the digital acceleration signal with the absolute value of the previous digital acceleration signal, and compute a so-called xe2x80x9cdelta-jerkxe2x80x9d value corresponding thereto. The delta-jerk value is compared thereafter at step 210 with a Max value. If delta-jerk is less than Max value, algorithm execution advances to step 214 to inhibit airbag deployment. If, on the other hand, the delta-jerk value is greater than or equal to the Max value at step 210, algorithm execution advances to step 212 where the delta-jerk value is compared to a Min value. If the delta-jerk value is less than or equal to the Min value, algorithm execution advances to step 214 to inhibit airbag deployment. If, however, the delta-jerk value is greater than the Min value at step 212, algorithm execution advances to step 216 where microprocessor 190 is operable to determine whether the digital acceleration signal is stuck to rail or ground by comparing the digital acceleration signal with upper and lower boundary values. Thereafter at steps 218 and 220, algorithm 200 is operable to advance to step 214 to inhibit airbag deployment if the digital acceleration signal is outside the upper or lower boundary values, and otherwise advances to step 222 to deploy the airbag 174.
The airbag calculation/deployment algorithm 200 of FIG. 3 is operable to process the digital acceleration signal to determine whether airbag deployment is warranted, and if so to monitor the time rate of change of the digital acceleration signal to determine whether to inhibit airbag deployment. The steps of algorithm 200 monitoring the time rate of change of the digital acceleration signal and comparing this value to maximum and minimum threshold values accomplish in software the function of the arming sensor 110 of the system 100 of FIG. 1. Step 210 inhibits airbag deployment in cases where the absolute value of the digital acceleration signal minus the previous digital signal is greater than the Max threshold, wherein such conditions are typically indicative of an output fault since true crash signal levels generally do not move fast enough to produce such large differences between signal values. Step 212 similarly inhibits airbag deployment in cases where the absolute value of the digital acceleration signal minus the previous digital signal is less than the Min threshold, wherein such conditions are typically indicative of an output fault since true crash data shows at least some minimum movement in the magnitude of the acceleration signals over time.
One drawback associated with the use of a software algorithm, such as algorithm 200, to detect deployment inhibit conditions is that such algorithms typically require a microprocessor to perform sophisticated calculations associated with at least the determination of the difference values. Requiring a microprocessor, in turn, increases the cost and complexity of airbag deployment discrimination systems. Generally, a microprocessor is not needed to accomplish the stuck-to-rail and stuck-to-ground comparisons of steps 216-220 since such steps are easily implemented in hardware with comparators. Likewise, a microprocessor is not needed to execute the deployment control algorithm 152 since supplemental inflatable restraint control systems are known that do not include a microprocessor but instead includes analog circuitry operable to execute in hardware an analog version of algorithm 152. One such control system is described in U.S. Pat. No. 5,801,619 which is assigned to the assignee of the present invention, and the contents of which are incorporated herein by reference.
The delta-jerk calculation of step 208, on the other hand, is not so easily realizable in hardware circuitry. On possible solution to this dilemma is to provide one or more microprocessors for executing at least the error detection functions (e.g., inhibit features of algorithm 192), but this would generally be cost prohibitive. An ideal solution to the foregoing problem would be to conduct the error detection functions; i.e., the airbag deployment inhibit features of steps 208-220 of algorithm 200, without microprocessor involvement, and then do away with the microprocessor altogether by implementing a supplemental inflatable restraint control system of the type described in U.S. Pat. No. 5,801,619. What is therefore needed is an error detection circuit for accomplishing at least the error detection features performed heretofore by either an arming accelerometer or a microprocessor executable control algorithm. Ideally, such a circuit should not delay airbag deployment under valid crash conditions of sufficient severity to warrant airbag deployment, and should generally be operable to inhibit airbag deployment for a number of different error conditions as well as other invalid crash events.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, an error detection circuit for an airbag deployment control system comprises a delay circuit receiving an analog acceleration signal and producing a delay signal corresponding to the analog acceleration signal delayed in time, a differential circuit subtracting the delay signal from the analog acceleration signal and producing a difference signal corresponding thereto, and a first comparison circuit responsive to the difference signal to produce a first inhibit signal for inhibiting deployment of an airbag if the difference signal falls within a first predefined signal range.
In accordance with another aspect of the present invention, a method of inhibiting airbag deployment in an airbag deployment control system comprises the steps of receiving an analog acceleration signal over time, delaying the acceleration signal for a predefined time period and producing a delay signal corresponding thereto, subtracting the delay signal from the analog acceleration signal and producing a difference signal corresponding thereto, comparing the difference signal with a first signal window, and inhibiting deployment of an airbag if the difference signal falls within the first signal window.
One object of the present invention is to provide an error detection circuit for processing an analog acceleration signal and inhibiting airbag deployment under conditions wherein pending airbag deployment is the result of one or more error conditions and not the result of an actual crash event of sufficient severity to warrant airbag deployment.
Another object of the present invention is to provide such an error detection circuit for use with airbag deployment control systems that may or may not include a microprocessor-based airbag deployment control algorithm.
Yet another object of the present invention is to provide such an error detection circuit that does not delay airbag deployment under valid crash conditions of sufficient severity to warrant airbag deployment.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.